The Triumph Dolomite Club - Discussion Forum

Having recently revived my tr7 engine I have followed Jon Tilsons carb setup guide to try and get the old girl running nicely.
My problem has always been that the engine idles too high. I have the screws all the way out but it's probably still around 1400 rpm. Everything has been fully cleaned and reset again before I started setting them up again. Timing is currently set to 10 btdc without vacuum
Any advice welcome

Have the throttle discs (butterflies) been removed from the spindle shafts? They go through a slot in the shaft and are locked in place by two small screws. If they aren't DEAD centre some air leaks round them and causes a high idle.

I had this after I rebuilt my SUs. The trick is to slacken the screws and let the discs find their own position before tightening them carefully. It worked for me.

Bumpa wrote: ↑Sun Nov 29, 2020 1:38 pm Have the throttle discs (butterflies) been removed from the spindle shafts? They go through a slot in the shaft and are locked in place by two small screws. If they aren't DEAD centre some air leaks round them and causes a high idle.

I had this after I rebuilt my SUs. The trick is to slacken the screws and let the discs find their own position before tightening them carefully. It worked for me.

That would be my suggestion as well, it only needs a tiny gap around the butterfly to cause chaos.

If the butterflies aren't the problem, are the levers clamped on the spindle between the two carbs, and operated by the throttle linkage, holding the butterflies open even when there's slack in the cable and the idle screws are fully withdrawn? If they are fully off the actuating arms on the butterfly spindles, and the idle is still high, it nearly has to be the butterflies.

I don't believe in undoing the clamps on those arms just to set the idle. But after a full rebuild, it's probably worth the pain in re-setting them. Its far more important that those arms operate the two carbs the same as the accelerator pedal is pressed than it is to get the two carbs balanced on idle - it's just idle FFS.

Graham

I'm very grateful for the quick replies . The advice on here is always appreciated. I will check both suggestions and report back

Andy

Hello, have you considered worn spindle bushes? My car had a similar issue and it was due to air getting past the spindle bushes. It makes a lean mixture and high idle. Easy to test, with the engine idling spray some carb cleaner on the spindle bushes of both carbs - Be careful not to set fire to the car. If they are leaking the spray will temporarily block the gap and the idle will drop. It will increase again when all the spray has been drawn through. New bushes and machining are about £60.

Good luck

Another possible cause, if the the butterfly discs are fitted with poppet valves, is that a poppet valve is a spring loaded disc which is supposed to open when the butterfly snaps shut to bleed a little mixture through and prevent stalling and backfiring. They often start to leak and cause problems with the idle. I believe most owners now fit plain butterfly disc or solder up the poppet valves. Below is a photo of a disc with a poppet valve fitted.

TFN wrote: ↑Sun Nov 29, 2020 4:51 pm spray some carb cleaner on the spindle bushes of both carbs

What's wrong with WD40?

One further thing to check is the fast idle adjustment screws under the linkages, if they've been screwed up too far, it'll never idle slow!

Steve

Cheers all
Hoping to check today.
The fast idle screws are ok, set about 1.5mm back from the choke linkage. I did undo the throttle clamps last night and the spindle on each carb moved back very slightly which could indicate the butterflies were open a tiny bit.
With regards to the poppet valves I'm pretty sure that being a skinflint , I glued them solid with JB weld some years ago rather than replacing them.
Maybe it's time to sort them properly

So initially, the idle has lowered a fraction. not sprayed anything around the spindle bushes as yet but will go back to that and see what happens.
I did notice today that the car didnt like the choke being on to start it despite being quite cold outside today. The choke literally would kill the running. So with the help of my son, i managed to keep the car running by me holding the throttle linkage open a little until it was warm.
so i was thinking it was too rich? on testing the carbs by lifting the damper a little on each one, the engine would again die. so i turned the jets down about ten flats each to richen it up enough so it was even, when lifting the damper.
on doing so the idle dropped again. so much so that it needed the idle screws adjusting to keep the engine running. (if a little lumpy).

I had been really pleased with myself, setting up the carbs using some of the guides on here, but now i feel i may have to start over again

I did away with the poppet valves on my 1850HL carbs and fitted solid discs. I also did away with the waxstat jets which improved the car enormously. Mine now starts and runs beautifully.

Sorry to be unhelpful, but it sounds like you might want to go back and start over from the beginning to check the basic setup. Something must be way off

And it might be something like the fix that xvivalve helped me out with below...

xvivalve wrote: ↑Fri Aug 07, 2020 7:35 pm There are two 7/16" AF bolts which hold the throttle bracket onto the inlet manifold; slacken these and you'll find there is slight adjustment in the alignment of the bracket. If it is not aligned properly, you'll find it can bizarrely hold one of the butterflies slightly open!

I agree with Russ, it's probably best to start again now the actuator clamps have been re-set. As to the linkage mounting bolts, if you re-set the two throttle actuator clamps after you've had the linkage or the carbs off, like you always should, that can never be a problem. I just don't reset them clamps every time I do the mix (like the Repair Operations Manual says you should) cos it I find it tricky to get it as equal as I want it to be.

I have also taken to using a vernier gauge to set the jets the same distance down from the step - as I remember 50 thou is recommended for a start. It does seem more accurate than trying to feel for the jets level with the steps the same and turning 12 flats down from there. But I don't know whether it matters enough.

Something else to consider is that I was having problems a while back setting the mixture so it was right at idle and under load. Turned out it was bunged-up K&Ns that even the red fuming nitric acid (from the safety instructions) K&N sell as cleaner wouldn't fix well enough. I still think £18 for a pair of stainless steel and foam filters from Watford Classics was reasonable, even allowing for the skin loss from the razor sharp edges and needing to add 4 M6 thin nuts to make assembly less of a pain.

Graham